Introduce helper functions for safe fork+exec of processes

In some situations, we want to execute an external shell command
in a non-blocking way.  Similar to 'system', but without waiting for
the child to complete.  We also want to close all file descriptors
ahead of the exec() and filter + modify the environment.

Change-Id: Ib24ac8a083db32e55402ce496a5eabd8749cc888
Related: OS#4332

3 files changed, 202 insertions, 0 deletions

diff --git a/tests/exec/exec_test.c b/tests/exec/exec_test.c
new file mode 100644
index 00000000..5f4b460c
--- /dev/null
+++ b/tests/exec/exec_test.c
@@ -0,0 +1,155 @@
+#include <osmocom/core/utils.h>
+#include <osmocom/core/exec.h>
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <unistd.h>
+#include <errno.h>
+
+static void env_dump(char **env)
+{
+	char **ent;
+
+	for (ent = env; *ent; ent++)
+		printf("\t%s\n", *ent);
+}
+
+static void test_env_filter(void)
+{
+	char *out[256];
+	char *env_in[] = {
+		"FOO=1",
+		"BAR=2",
+		"USER=mahlzeit",
+		"BAZ=3",
+		"SHELL=/bin/sh",
+		NULL
+	};
+	const char *filter[] = {
+		"SHELL",
+		"USER",
+		NULL
+	};
+	int rc;
+
+	printf("\n==== osmo_environment_filter ====\n");
+
+	printf("Input Environment:\n");
+	env_dump(env_in);
+	printf("Input Whitelist:\n");
+	env_dump((char **) filter);
+	rc = osmo_environment_filter(out, ARRAY_SIZE(out), env_in, filter);
+	printf("Output Environment (%d):\n", rc);
+	env_dump(out);
+	OSMO_ASSERT(rc == 3);
+
+	printf("Testing for NULL out\n");
+	rc = osmo_environment_filter(NULL, 123, env_in, filter);
+	OSMO_ASSERT(rc < 0);
+
+	printf("Testing for zero-length out\n");
+	rc = osmo_environment_filter(out, 0, env_in, filter);
+	OSMO_ASSERT(rc < 0);
+
+	printf("Testing for one-length out\n");
+	rc = osmo_environment_filter(out, 1, env_in, filter);
+	OSMO_ASSERT(rc == 1 && out[0] == NULL);
+
+	printf("Testing for no filter\n");
+	rc = osmo_environment_filter(out, ARRAY_SIZE(out), env_in, NULL);
+	OSMO_ASSERT(rc < 0);
+
+	printf("Testing for no input\n");
+	rc = osmo_environment_filter(out, ARRAY_SIZE(out), NULL, filter);
+	OSMO_ASSERT(rc == 1 && out[0] == NULL);
+	printf("Success!\n");
+}
+
+static void test_env_append(void)
+{
+	char *out[256] = {
+		"FOO=a",
+		"BAR=b",
+		"BAZ=c",
+		NULL,
+	};
+	char *add[] = {
+		"MAHL=zeit",
+		"GSM=global",
+		"UMTS=universal",
+		"LTE=evolved",
+		NULL,
+	};
+	int rc;
+
+	printf("\n==== osmo_environment_append ====\n");
+
+	printf("Input Environment:\n");
+	env_dump(out);
+	printf("Input Addition:\n");
+	env_dump(add);
+	rc = osmo_environment_append(out, ARRAY_SIZE(out), add);
+	printf("Output Environment (%d)\n", rc);
+	env_dump(out);
+	OSMO_ASSERT(rc == 8);
+	printf("Success!\n");
+}
+
+static void test_close_fd(void)
+{
+	struct stat st;
+	int fds[2];
+	int rc;
+
+	printf("\n==== osmo_close_all_fds_above ====\n");
+
+	/* create some extra fds */
+	rc = socketpair(AF_UNIX, SOCK_STREAM, 0, fds);
+	OSMO_ASSERT(rc == 0);
+
+	rc = fstat(fds[0], &st);
+	OSMO_ASSERT(rc == 0);
+
+	osmo_close_all_fds_above(2);
+
+	rc = fstat(fds[0], &st);
+	OSMO_ASSERT(rc == -1 && errno == EBADF);
+	rc = fstat(fds[1], &st);
+	OSMO_ASSERT(rc == -1 && errno == EBADF);
+	printf("Success!\n");
+}
+
+static void test_system_nowait(void)
+{
+	char *addl_env[] = {
+		"MAHLZEIT=spaet",
+		NULL
+	};
+	int rc, pid, i;
+
+	printf("\n==== osmo_system_nowait ====\n");
+
+	pid = osmo_system_nowait("env | grep MAHLZEIT 1>&2", osmo_environment_whitelist, addl_env);
+	OSMO_ASSERT(pid > 0);
+	for (i = 0; i < 10; i++) {
+		sleep(1);
+		rc = waitpid(pid, NULL, WNOHANG);
+		if (rc == pid) {
+			printf("Success!\n");
+			return;
+		}
+	}
+	printf("ERROR: child didn't terminate within 10s\n");
+}
+
+int main(int argc, char **argv)
+{
+	test_env_filter();
+	test_env_append();
+	test_close_fd();
+	test_system_nowait();
+
+	exit(0);
+}
diff --git a/tests/exec/exec_test.err b/tests/exec/exec_test.err
new file mode 100644
index 00000000..4edc61d6
--- /dev/null
+++ b/tests/exec/exec_test.err
@@ -0,0 +1 @@
+MAHLZEIT=spaet
diff --git a/tests/exec/exec_test.ok b/tests/exec/exec_test.ok
new file mode 100644
index 00000000..45a20f07
--- /dev/null
+++ b/tests/exec/exec_test.ok
@@ -0,0 +1,46 @@
+
+==== osmo_environment_filter ====
+Input Environment:
+	FOO=1
+	BAR=2
+	USER=mahlzeit
+	BAZ=3
+	SHELL=/bin/sh
+Input Whitelist:
+	SHELL
+	USER
+Output Environment (3):
+	USER=mahlzeit
+	SHELL=/bin/sh
+Testing for NULL out
+Testing for zero-length out
+Testing for one-length out
+Testing for no filter
+Testing for no input
+Success!
+
+==== osmo_environment_append ====
+Input Environment:
+	FOO=a
+	BAR=b
+	BAZ=c
+Input Addition:
+	MAHL=zeit
+	GSM=global
+	UMTS=universal
+	LTE=evolved
+Output Environment (8)
+	FOO=a
+	BAR=b
+	BAZ=c
+	MAHL=zeit
+	GSM=global
+	UMTS=universal
+	LTE=evolved
+Success!
+
+==== osmo_close_all_fds_above ====
+Success!
+
+==== osmo_system_nowait ====
+Success!